11 Mar 2016

A new type of graphene-based filter could be the key to managing the global water crisis, a study has revealed. The new graphene filter, which has been developed by Monash University and the University of Kentucky, allows water and other liquids to be filtered nine times faster than the current leading commercial filter.

According to the World Economic Forum’s Global Risks Report, lack of access to safe, clean water is the biggest risk to society over the coming decade. Yet some of these risks could be mitigated by the development of this filter, which is so strong and stable that it can be used for extended periods in the harshest corrosive environments, and with less maintenance than other filters on the market.

The research team was led by Associate Professor Mainak Majumder from Monash University. Associate Professor Majumder said the key to making their filter was developing a viscous form of graphene oxide that could be spread very thinly with a blade.

This technique allows the filters to be produced much faster and in larger sizes, which is critical for developing commercial applications. The graphene-based filter could be used to filter chemicals, viruses, or bacteria from a range of liquids. It could be used to purify water, dairy products or wine, or in the production of pharmaceuticals.

This is the first time that a graphene filter has been able to be produced on an industrial scale – a problem that has plagued the scientific community for years.

Research team member and PhD candidate, Abozar Akbari, said scientists had known for years that graphene filters had impressive qualities, but in the past they had been difficult and expensive to produce.

“It’s been a race to see who could develop this technology first, because until now graphene-based filters could only be used on a small scale in the lab,” Mr Akbari said.

Graphene is a lattice of carbon atoms so thin it’s considered to be two-dimensional. It has been hailed as a “wonder-material” because of its incredible performance characteristics and range of potential applications.

The team’s new filter can filter out anything bigger than one nanometre, which is about 100,000 times smaller than the width of a human hair.

The research has gathered interest from a number of companies in the United States and the Asia Pacific, the largest and fastest-growing markets for nano-filtration technologies.

The team’s research was supported by industry partner Ionic Industries, as well as a number of Australian Research Council grants.

Ionic Industries’ CEO, Mark Muzzin, said the next step was to get the patented graphene-based filter on the market.

“We are currently developing ways to test how the filter fares against particular contaminants that are of interest to our customers” Mr Muzzin said.

Co-author of the research and Director of the Center for Membrane Science, Professor Dibakar Bhattacharyya, from the University of Kentucky, said: “The ability to control the thickness of the filter and attain a sharper cut-off in separation, and the use of only water as the casting solvent, is a commercial breakthrough.”

03 Nov 2015

With the intensifying drought in California, the state has accelerated the construction of desalination plants. Yet due to high construction and operating costs, as well as environmental concerns, we’re not likely to see reclaimed seawater represent more than a small fraction of America’s clean water reserves for some time to come. Aside from other costs, the immense amounts of energy required to make clean water from seawater continues to make desalination a niche solution in most parts of the world.

When Jeffrey Grossman, a professor at MIT’s Department of Materials Science and Engineering (DMSE), began looking into whether new materials might reduce the cost of desalination, he was surprised to find how little research and development money was being applied to the problem.

“A billion people around the world lack regular access to clean water, and that’s expected to more than double in the next 25 years,” Grossman says. “Desalinated water costs five to 10 times more than regular municipal water, yet we’re not investing nearly enough money into research. If we don’t have clean energy we’re in serious trouble, but if we don’t have water we die.”

At the Grossman Group, which explores the development of new materials to address clean energy and water problems, a possible solution may be at hand. Grossman’s lab has demonstrated strong results showing that new filters made from graphene could greatly improve the energy efficiency of desalination plants while potentially reducing other costs as well.

Graphene, which results from slicing off an atom-thick layer of graphite, is increasingly emerging as something of a wonder material. The Grossman Group, for example, is also looking into using it as a cheaper alternative to silicon for making solar cells.

“It’s never been a more exciting time to be a materials scientist,” says Grossman. “When you look at clean tech or water filtration, you find that the energy conversion bottleneck stems from the material. We can now design materials pretty much all the way down to the scale of the atom in almost any way we want, tailoring materials in ways that were previously impossible. There’s a convergence emerging in which we are facing enormously pressing problems that can only be solved by developing new materials.”

Graphene filters: Up to 50 percent less energy

First isolated in 2003, graphene has different electrical, optical, and mechanical properties than graphite. “It’s stronger than steel, and it has unique sieving properties,” Grossman says. At only an atom thick, there’s far less friction loss when you push seawater through a perforated graphene filter compared with the polyamide plastic filters that have been used for the last 50 years, he says.

“We have shown that perforated graphene filters can handle the water pressures of desalination plants while offering hundreds of times better permeability,” Grossman explains. “The process of pumping seawater through filters represents about half the operating costs of a desalination plant. With graphene, we could use up to 50 percent less energy.”

Another advantage is that graphene filters don’t become fouled with bio-growth at nearly the rate that occurs with polyamide filters. Desalination plants often run at reduced efficiency due to the need to frequently clean the filters. In addition, the chlorine used to clean the filters reduces the structural integrity of the polyamide, requiring frequent replacement. By comparison, graphene is resistant to the damaging effects of chlorine.

According to Grossman, you could easily replace polyamide filters with graphene filters in existing plants. Like polyamide filters, graphene filters can be mounted on robust polysulfone supports, which have larger holes that sieve out particulates.

“We have shown that perforated graphene filters can handle the water pressures of desalination plants while offering hundreds of times better permeability,” Grossman explains. “The process of pumping seawater through filters represents about half the operating costs of a desalination plant. With graphene, we could use up to 50 percent less energy.”

Another advantage is that graphene filters don’t become fouled with bio-growth at nearly the rate that occurs with polyamide filters. Desalination plants often run at reduced efficiency due to the need to frequently clean the filters. In addition, the chlorine used to clean the filters reduces the structural integrity of the polyamide, requiring frequent replacement. By comparison, graphene is resistant to the damaging effects of chlorine.

According to Grossman, you could easily replace polyamide filters with graphene filters in existing plants. Like polyamide filters, graphene filters can be mounted on robust polysulfone supports, which have larger holes that sieve out particulates.

Yet, significant challenges remain in bringing down costs. The Grossman Group has made good progress in creating high volumes of graphene at a reasonably low cost. A more serious challenge, however, is cost-effectively poking uniform holes in the graphene in a highly scalable manner.

“A typical plant has tens of thousands of membranes, configured in two-meter long tubes, each of which has 40 square meters of rolled up active membrane,” Grossman says. “We have to match that volume at the same cost, or it’s a nonstarter.”

Making graphene on the cheap

The traditional way to make graphene—since its first isolation in 2003, mind you—is to peel it off with adhesive. “You literally take a piece of Scotch Tape to graphite and you peel,” Grossman explains. “If you keep doing this, you eventually wind up with a single layer. The problem is it would take forever to peel off enough graphene for a desalination plant.”

Another approach is to “grow” graphene by applying super-hot gases to copper foil. “Growing graphene provides the best quality, which is why the semiconductor industry is interested in it,” Grossman says. The process, however, is very expensive and energy-intensive.

Instead, the Grossman Group is using a much more affordable chemical approach, which produces sufficient quality for creating desalination membranes. “Fortunately, our application doesn’t require the best quality,” says Grossman. “With the chemical technique, we put graphite in a solution, and apply low temperature chemistry to break apart the entire chunk of graphite into sheets. We can get lots of graphene very cheaply and quickly.”

Creating pores that block salt but let water molecules pass is a steeper challenge. The reason desalination is possible in the first place is that when diffused in water, salt ions bond with water molecules, thereby creating a larger entity. But the difference in size compared to a free water molecule is still frustratingly small.

“The challenge is to find the sweet spot of about 0.8 nanometers,” Grossman says. “If your pores are at 1.5 nm, then both the water and salt will pass through. If they’re half a nanometer, then nothing gets through.”

A 0.8 nm hole is “smaller than we’ve ever been able to make in a controllable way with any other material,” Grossman says. “And we need to do this over a very large area very consistently and cheaply.”

The Grossman Group is pursuing three techniques to make nanoporous graphene membranes, all of which use chemical and thermal energy rather than mechanical processes. “If you tried to use lithography, it would take years,” Grossman says. “Our first approach involves making the holes too big, and then carefully filling them in. Another tries to make them exactly the right size, and the third involves starting with a material without holes and then carefully ripping it apart.”

The chemical technique for making graphene actually produces graphene oxide, which is considered undesirable for semiconductors, but is fine for filters. As a result, the researchers were able to avoid the difficult step of removing the oxygen from the graphene oxide. In fact, they found a way to use the oxygen to their advantage.

“By controlling the way the oxygen is bonded to the graphene sheet, we can use chemical and thermal energy to drill the holes with the help of the oxygen,” Grossman says.

First target: Brackish water

As the Grossman Group continues to work on the challenge of manufacturing and perforating graphene sheets, Grossman is looking to leverage other benefits of graphene filters to help bring the technology to market.

Although graphene should improve efficiency with seawater and the even saltier, dirtier water used in hydraulic fracturing, it will likely debut in plants that clean brackish water, such as found in estuaries. “It turns out that higher permeability even by a factor of two or three would make a bigger difference with brackish water than with seawater,” Grossman says. “You lower the energy consumption in both cases, but more so for brackish water.”

Graphene filters could also enable the construction of smaller, cheaper plants. “With graphene you have more choices in how you operate the plant,” Grossman says. “You could apply the same pressures but get more water out, or you could operate it at lower pressures and get the same amount of water, but at a lower energy cost.”

Grossman notes that it can take years or even decades to site and permit a plant in heavily populated coastal areas. “A lot of effort goes into how you’re going to build the plant and where you’re going to find enough land,” Grossman says. “Having the option to build a smaller plant would be a big advantage.”

NEWT Center will use nanotechnology to transform economics of water treatment A Rice University-led consortium of industry, university and government partners has been chosen to establish one of the National Science Foundation’s (NSF) prestigious Engineering Research Centers in Houston to develop compact, mobile, off-grid water-treatment systems that can provide clean water to millions of people who lack it and make U.S. energy production more sustainable and cost-effective.

Nanotechnology Enabled Water Treatment Systems, or NEWT, is Houston’s first NSF Engineering Research Center (ERC) and only the third in Texas in nearly 30 years. It is funded by a five-year, $18.5 million NSF grant that can be renewed for a potential term of 10 years. NEWT brings together experts from Rice, Arizona State University, Yale University and the University of Texas at El Paso (UTEP) to work with more than 30 partners: including Shell, Baker Hughes, UNESCO, U.S. Army Corps of Engineers and NASA.

ERCs are interdisciplinary, multi-institutional centers that join academia, industry and government in partnership to produce both transformational technology and innovative-minded engineering graduates who are primed to lead the global economy. ERCs often become self-sustaining and typically leverage more than $40 million in federal and industry research funding during their first decade.

“The importance of clean water to global health and economic development simply cannot be overstated,” said NEWT Director Pedro Alvarez, the grant’s principal investigator. “We envision using technology and advanced materials to provide clean water to millions of people who lack it and to enable energy production in the United States to be more cost-effective and more sustainable in regard to its water footprint.”

NEWT Center will use nanotechnology to transform water treatment: Video

Houston-area Congressman John Culberson, R-Texas, chair of the House Subcommittee on Commerce, Justice and Science, said, “Technology is a key enabler for the energy industry, and NEWT is ideally located at Rice, in the heart of the world’s energy capital, where it can partner with industry to ensure that the United States remains a leading energy producer.”

Alvarez, Rice’s George R. Brown Professor of Civil and Environmental Engineering and professor of chemistry, materials science and nanoengineering, said treated water is often unavailable in rural areas and low-resource communities that cannot afford large treatment plants or the miles of underground pipes to deliver water. Moreover, large-scale treatment and distribution uses a great deal of energy. “About 25 percent of the energy bill for a typical city is associated with the cost of moving water,” he said.

NEWT Deputy Director Paul Westerhoff said the new modular water-treatment systems, which will be small enough to fit in the back of a tractor-trailer, will use nanoengineered catalysts, membranes and light-activated materials to change the economics of water treatment.

“NEWT’s vision goes well beyond today’s technology,” said Westerhoff, vice provost of academic research at ASU and co-principal investigator on the NSF grant. “We’ve set a path for transformative new technology that will move water treatment from a predominantly chemical treatment process to more efficient catalytic and physical processes that exploit solar energy and generate less waste.”

Co-principal investigator and NEWT Associate Director for Research Qilin Li, the leader of NEWT’s advanced treatment test beds at Rice, said the system’s technology will be useful in places where water and power infrastructure does not exist.

“The NEWT drinking water system will be able to produce drinking water from any source, including pond water, seawater and floodwater, using solar energy and even under cloudy conditions,” said Li, associate professor of civil and environmental engineering, chemical and biomolecular engineering, and of materials science and nanoengineering at Rice. “The modular treatment units will be easy to configure and reconfigure to meet desired water-quality levels. The system will include components that target suspended solids, microbes, dissolved contaminants and salts, and it will have the ability to treat a variety of industrial wastewater according to the industry’s need for discharge or reuse.”

NEWT will focus on applications for humanitarian emergency response, rural water systems and wastewater treatment and reuse at remote sites, including both onshore and offshore drilling platforms for oil and gas exploration.

Yale’s Menachem “Meny” Elimelech, co-principal investigator and lead researcher for membrane processes, said NEWT’s innovative enabling technologies are founded on rigorous basic research into nanomaterials, membrane dynamics, photonics, scaling, paramagnetism and more.

“Our modular water-treatment systems will use a combination of component technologies,” said Elimelech, Yale’s Roberto C. Goizueta Professor of Environmental and Chemical Engineering. “For example, we expect to use high-permeability membranes that resist fouling; engineered nanomaterials that can be used for membrane surface self-cleaning and biofilm control; capacitive deionization to eliminate scaly mineral deposits; and reusable magnetic nanoparticles that can soak up pollutants like a sponge.”

UTEP’s Jorge Gardea-Torresdey, co-principal investigator and co-leader of NEWT’s safety and sustainability effort, said the rapid development of engineered nanomaterials has brought NEWT’s transformative vision within reach.

“Treating water using fewer chemicals and less energy is crucial in this day and age,” said Gardea-Torresdey, UTEP’s Dudley Professor of Chemistry and Environmental Science and Engineering. “The exceptional properties of engineered nanomaterials will enable us to do this safely and effectively.”

Alvarez said another significant research thrust in nanophotonics will be headed by Rice co-principal investigator Naomi Halas, the inventor of “solar steam” technology, and co-led by ASU’s Mary Laura Lind.

“More than half of the cost associated with desalination of water comes from energy,” said Halas, Rice’s Stanley C. Moore Professor of Electrical and Computer Engineering and professor of chemistry, bioengineering, physics and astronomy, and materials science and nanoengineering. “We are working to develop several supporting technologies for NEWT, including nanophotonics-enabled direct solar membrane distillation for low-energy desalination.”

Rice’s Michael Wong, Yale’s Jaehong Kim and UTEP’s Dino Villagran will collaborate in efforts to develop novel multifunctional materials such as superior sorbents and catalysts, and Yale’s Julie Zimmerman will co-lead cross-cutting efforts in safety and sustainability. Rice’s Roland Smith will lead a comprehensive diversity program that aims to attract more women and underrepresented minority students and faculty, and Rice’s Brad Burke will head up innovation and commercialization efforts with private partners. Rice’s Rebecca Richards-Kortum will lead an innovative educational program that incorporates some of the “experiential learning” techniques she developed for the award-winning undergraduate research programs at Rice 360º: Institute for Global Health Technologies, and Rice’s Carolyn Nichol will lead the K-12 education efforts.

Alvarez said NEWT’s goal is to attract industry funding and become self-sufficient within 10 years. Toward that end, he said NEWT was careful to select industrial partners from every part of the water market, including equipment makers and vendors, system operators, industrial service firms and others.

NEWT is one of three new ERCs announced by the NSF today in Washington. They join 16 existing centers that are still receiving federal support, including Texas’ only other active ERC, the University of Texas at Austin’s NASCENT, as well as the other active center in which Rice is a partner, Princeton University’s MIRTHE.

Alvarez credited Culberson and the Texas Railroad Commission for helping facilitate partnerships that were crucial for NEWT. He said the consortium’s bid to land the NSF grant was also made possible by seed funding from Rice’s Energy and Environment Initiative, a sweeping institutional initiative to engage Rice faculty from all disciplines in creating sustainable, transformative energy technologies.

“Rice’s Energy and Environment Initiative was instrumental in developing a competitive proposal, in facilitating a team-building effort and in facilitating contacts with industry to get the necessary buy-in for our vision,” Alvarez said.

Illness-inducing bacteria, meet nano-engineered cotton–and a quick death. Researchers have created a new “filter” that zaps bacteria with electric fields to clean drinking water. They say their system may find use in developing countries since it requires only a small amount of voltage (a couple of car batteries, a stationary bike, or a solar panel could do the job) and cleans water an estimated 80,000 times faster than traditional devices.

Instead of trapping bacteria in small pores like many slow-going traditional filters, the cotton and silver nanowire combo uses small electric currents running through the nanowires to kill the bacteria outright. In a paper to appear in the journal Nano Lettersresearchers say that 20 volts and 2.5 inches worth of the material killed 98 percent of Escherichia coli in the water they tested in their lab setup.

The authors argue that the filter’s silver nanowires and carbon nanotubes are cheap; the small amount of silver required makes its expense “negligible,” coauthor Yi Cui says in a press release, and the group chose to use cotton because of its abundance.

They needed a foundation material that was “cheap, widely available and chemically and mechanically robust.” So they went with ordinary woven cotton fabric. “We got it at Wal-mart,” Cui said. [Stanford University]

They made the potent combination by dipping the cotton first in a “broth” containing carbon nanotubes and then the silver nanowires, allowing the structures to coat the cotton fibers. The scanning electron microscope image above shows the silver nanowires compared to the large cotton fibers (the red line is 10 microns long). The current running though the material, a few milliamperes, may be fatal for the bacteria but it would barely makes a human tingle.

[B]ecause the voltage is so low, it doesn’t require serious electricity generation. A person could generate the power from a stationary bike or a hand-cranked device. No pumping is required either. The force of gravity is enough to allow the water and its nasties to pass through the cotton and get zapped! [Discovery News]

Next, the group hopes to test the device on other microorganisms–perhaps those responsible for other waterborne illness such as cholera, typhoid and hepatitis. The researchers will also continue testing the filter to make sure only clean water comes out and not any nano-structures.

“So far, our evidence suggests that they don’t come off,” Cui told New Scientist. “It is an interesting academic study,” says nanoengineer Eric Hoek at the University of California, Los Angeles. He says proving that the potentially harmful CNTs [carbon nanotubes] do not leach into the water will be a key step in finding out if it is useful on a practical level. [New Scientist]

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